Ousted Pakistani Prime Minister Nawaz Sharif and his daughter Maryam were arrested on Friday after flying back to the country to face lengthy prison sentences.

Sharif and his daughter were convicted and sentenced in absentia to ten and seven years, respectively, in a corruption case.

The two were in London visiting Sharif’s ailing wife when a Pakistani court convicted them of corruption and sent them to prison.

The officials spoke on condition of anonymity because they were not authorised to brief the media.

Sharif’s son-in-law is currently serving his one-year prison sentence on the same charge, which stems from the purchase of luxury flats in Britain that the court said were bought with illegally-earned money.

Sharif is expected to appeal his conviction and seek bail.

Before his return, police swept through Lahore, arresting scores of Sharif’s Pakistan Muslim League party workers to prevent them from greeting him at the airport.

In a video message on Friday reportedly from his aircraft en route to Pakistan, Sharif said he was returning knowing he would be taken directly to prison.

Sharif has been banned from taking part in politics, and his brother Shahbaz Sharif now heads his Pakistan Muslim League and is fighting for re-election on July 25.

In a televised appeal to supporters from London earlier this week, Sharif criticised Pakistan’s powerful military, which has ruled the country directly or indirectly for most of its 71-year history, saying Pakistan now has a “state above the state”.

Pakistani and international rights groups have accused the military of trying to maintain its influence in Pakistani politics by keeping Sharif out of power. The military denied the accusations saying its help in carrying out the elections was requested by Pakistan’s Election Commission. The army will deploy 350,000 security personnel to polling stations throughout the country on election day.

Underscoring the security threat, a bomb killed at least 70 people on Friday during a rally in Pakistan’s restive Balochistan province – the day’s second attack on a political event in Mastung town, near the provincial capital of Quetta.

Earlier a bomb blast struck the convoy of Akram Khan Durrani, an ally of Sharif’s PML-N from the religious Muttahida Majlis-e-Amal party (MMA) in the northern town of Bannu, killing four people.

The MMA is expected to challenge Imran Khan’s PTI in the northern Khyber Pakhtunkhwa province in the upcoming polls.

The explosion also wounded 20 people and the candidate escaped unharmed, said local police chief Rashid Khan.

Durrani had just finished his speech when the bomb exploded.

Khan, who hopes to become the next prime minister, condemned Friday’s attack. In a tweet, he said there seems to be a conspiracy to sabotage the July 25 vote. But he said the people of Pakistan will not allow anything to prevent “historic” elections from taking place.